Serpentine

Hardness: 2.5-4.0 on the Mohs scale (relatively soft). Color: Varies greatly, most commonly shades of green (light green, yellowish-green, dark green, blackish-green), but can also be white, gray, yellow, brown, or red. Luster: Greasy, waxy, or silky to dull. Crystal Structure: Monoclinic, but typically found in massive, platy, or fibrous aggregates. Cleavage: Perfect basal cleavage in one direction, though not always apparent in massive forms. Specific Gravity: 2.5-2.6.

Serpentine forms through the serpentinization of ultramafic rocks (like peridotite and dunite) and mafic rocks (like basalt and gabbro). This process involves hydrothermal alteration where water reacts with magnesium and iron-rich silicate minerals (like olivine and pyroxene) at low to moderate temperatures and pressures. This alteration results in the formation of various serpentine group minerals. The process can occur in oceanic crust settings (mid-ocean ridges, subduction zones) or within continental crust, often associated with tectonic activity. Its geological age varies widely depending on the age of the parent rocks and the timing of the metamorphic event.

Industry: Historically, some forms (chrysotile) were used as asbestos due to their heat resistance and insulating properties. Currently, non-asbestiform serpentine is used as an industrial filler (e.g., in paints, plastics), a source of magnesium, and as a decorative aggregate. Jewelry/Construction: Used as an ornamental stone for carving, sculptures, and architectural elements (e.g., tiling, countertops, facing stone) due to its attractive color and ease of carving. It is sometimes marketed as 'New Jade' or 'Verde Antique'.

Serpentine is named after the serpents due to its mottled green color resembling a snake's skin. It is often confused with jade due to similar appearance, but serpentine is softer. Some varieties of serpentine containing chrysotile asbestos were historically used in construction, but the use of asbestos is now heavily regulated or banned due to health risks. Other safe, non-asbestiform varieties continue to be used as ornamental stones.

Identification in the field: Serpentine is characterized by its greasy or soapy feel, varied green color, and generally low hardness (can be scratched with a knife or even a copper coin, depending on the specific mineral in the group). It often exhibits a mottled or veined appearance. Common locations: Found globally in areas with abundant ultramafic and mafic rocks that have undergone hydrothermal alteration, such as California (USA), Canada, the Urals (Russia), Italy, New Zealand, and parts of the Middle East. Tips for collectors: Be aware that some fibrous varieties may be asbestos (chrysotile), which poses health risks if disturbed. Therefore, it's generally safer to collect massive, non-fibrous forms. Observe its characteristic feel and relative softness to distinguish it from tougher, harder minerals like jade.